The objective of this proposed program will be to develop a direct method for measurement of low density lipoprotein (LDL) cholesterol in plasma and serum using three-phase systems. LDL's are involved in the pathogenesis of coronary artery disease, and by lowering blood levels of LDL cholesterol one can reduce the risk of heart attack. For this reason, there has been considerable clinical and epidemiological interest in its measurement. Three-phase systems are formed when solvent is mixed with three soluble, non-toxic polymers. The three phases can separate biomolecules based on their physical and chemical properties. The experimental procedure will be aimed at determining the three-phase system conditions in which the LDL cholesterol is partitioned to one phase. The LDL cholesterol can then be removed from the system and quantified using established chemical and enzymatic techniques. Three-phase systems offer substantial benefits over competitive technology for direct LDL cholesterol measurement, such as ultracentrifugation. The proposed method is rapid, cost-effective and can be readily applied to large population studies.